Python3.10字符串转float报ValueError问题修复方案

在Python 3.10环境下运行分数计算代码时，预期逻辑为：用户输入字符串、字母等非数字内容时，程序返回重新输入环节，打印提示must be a number and bigger than 0 and less than 100。实际运行时程序会直接终止退出。

原有代码如下：

import time

def main():
    num1 = input("your t76ely\n")
    num2 = input("your num2\n")
    school = input("your school\n")

    num1 = float(num1)
    num2 = float(num2)
    school = float(school)

    if num1 > 100:
        print("must be a number and bigger than 0 and less than 100")
        while True:
            time.sleep(1)
            main()
    elif num1 < 0:
        print("must be a number and bigger than 0 and less than 100")
        while True:
            time.sleep(1)
            main()
    if num2 > 100:
        print("must be a number and bigger than 0 and less than 100")
        while True:
            time.sleep(1)
            main()
    elif num2 < 0:
        print("must be a number and bigger than 0 and less than 100")
        while True:
            time.sleep(1)
            main()
    if school > 100:
        print("must be a number and bigger than 0 and less than 100")
        while True:
            time.sleep(1)
            main()
    elif school < 0:
        print("must be a number and bigger than 0 and less than 100")
        while True:
            time.sleep(1)
            main()
    else:
        r = (40 % 100 * float(num1)) + (30 % 100 * float(num2)) + (30 % 100 * float(school))
    r = r / 100
    print(r)
    print('\nnum1 :', {num1}, '\nnum2 :', {num2}, "\nschool :", {school})

while True:
    main()
    if input("\nWant To continue ? Y/N\n").upper().strip() != "Y":
        break

输入名字trais、单个字母或任意字符串时，程序抛出如下错误：

Traceback (most recent call last):
  File "D:\Python Projects\your mark\mark calculator.py", line 51, in <module>
    main()
  File "D:\Python Projects\your mark\mark calculator.py", line 9, in main
    num1 = float(num1)
ValueError: could not convert string to float: 'trais'

• 代码直接调用float()转换用户输入内容，没有捕获非数字输入触发的ValueError异常，这是输入字符串后程序直接崩溃的核心原因。
• 原有校验逻辑存在冗余和设计缺陷：重复编写了多段结构完全一致的范围判断代码，输入非法时采用递归调用main()+死循环的写法，运行久了会触发递归栈溢出；权重计算部分40 % 100属于无效写法，计算结果和直接写40没有区别。

1. 抽取独立的分数输入校验函数，统一处理输入转换、范围校验逻辑，避免重复代码。
2. 用try-except语句捕获float()转换抛出的ValueError，输入非法时打印提示，等待1秒后循环要求用户重新输入，直到拿到合法的0-100之间的分数再返回。
3. 删除冗余的递归、无效死循环逻辑，简化分数权重计算写法。

修复后可正常运行的代码如下：

import time

def get_valid_score(prompt):
    while True:
        input_val = input(prompt)
        # 捕获非数字输入的转换异常
        try:
            score = float(input_val)
        except ValueError:
            print("must be a number and bigger than 0 and less than 100")
            time.sleep(1)
            continue
        # 校验数值范围
        if 0 <= score <= 100:
            return score
        print("must be a number and bigger than 0 and less than 100")
        time.sleep(1)

def main():
    num1 = get_valid_score("your t76ely\n")
    num2 = get_valid_score("your num2\n")
    school = get_valid_score("your school\n")

    # 按权重计算总分 40% num1 + 30% num2 + 30% school
    total_score = 0.4 * num1 + 0.3 * num2 + 0.3 * school
    print(total_score)
    print('\nnum1 :', num1, '\nnum2 :', num2, "\nschool :", school)

if __name__ == "__main__":
    while True:
        main()
        if input("\nWant To continue ? Y/N\n").upper().strip() != "Y":
            break

修复后效果：

• 输入非数字内容、超出0-100范围的数值时，都会打印指定提示，等待1秒后回到当前输入项要求重输，程序不会崩溃退出。
• 去掉了冗余代码和错误的递归逻辑，不会出现递归栈溢出问题，计算逻辑更简洁可读。

内容的提问来源于stack exchange，提问作者tra1s